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Measurement of the Hadronic Cross Section via Radiative Return at DA F NE

Measurement of the Hadronic Cross Section via Radiative Return at DA F NE. MENU 2004 September 3 rd Beijing, IHEP. Universität Karlsruhe Institut für Experimentelle Kernphysik. Achim Denig for the KLOE Collaboration. hep-ex/0407048, sent to Phys. Lett. B. Outline: Muon Anomaly

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Measurement of the Hadronic Cross Section via Radiative Return at DA F NE

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  1. Measurement of the Hadronic Cross Section via Radiative Return at DAFNE MENU 2004 September 3rd Beijing, IHEP Universität Karlsruhe Institut für Experimentelle Kernphysik Achim Denig for the KLOE Collaboration Achim Denig Radiative Return @ DAFNE MENU 2004

  2. hep-ex/0407048, sent to Phys. Lett. B • Outline: • Muon Anomaly • Radiative Return at KLOE • Results & Outlook Further KLOE-Results: St. Müller (Session B2) Achim Denig Radiative Return @ DAFNE MENU 2004

  3. HadronicVacuum Polarization 2nd largest contrib., cannot be calculated in pQCD Error of hadronic contribution is dominating total error ! Muon - Anomaly • Motivation: Determination of Hadronic Vacuum Polarization = High Precision Test of the Standard Model • Anomalous magnetic moment of the muon am = (g-2)m • Running fine structure constant at Z0-mass aQED(MZ) Dirac-Theory: (g - 2 ) = 0 Quantum corrections: (g - 2 )  0due to corrections of: - electromagnetic interaction - weak interaction - strong interaction (and maybe NEW PHYSICS ???) Achim Denig Radiative Return @ DAFNE MENU 2004

  4. H 1 / s2 makes low energy contributions especially important: in the range < 1 GeV contributes to 70% ! Hadronic Cross Section Hadronic contribution to amcan be estimated by means of a dispersion integral: - K(s) = analytic kernel-function, almost flat in s - above 2…5 GeV, use pQCD Input Dispersion Integral: a) hadronic electron-positron cross section data, e.g.e+e- p+ p- b) hadronic t- decays (CVC-theorem, taking into account isospin breaking corrections), e.g. t- p0 p-nt Achim Denig Radiative Return @ DAFNE MENU 2004

  5. Muon-Anomaly: Theory vs. Experiment Theoretical values taken from Davier, Eidelman, Höcker, Zhang: hep-ex/0308213 Status up to July ‘04 • Dispersion integral for hadronic • contribution to am evaluated for: • e+ e--Data ONLY • CMD-2 (VEPP-2M) measured p+ p- • channel with 0.6% precision < 1 GeV • 2.7s – Deviation • t-Data ONLY (if available) • ALEPH /OPAL/CLEO • 1.4s – Deviation e+e- data and t data differ for p+p- channel in a specific energy window above 0.6 GeV2 (above the r-peak)! THEORY ’20/‘03 Experiment BNL-E821 Values for m+(2002) and m-(2004) in agreement with each other. Precision:0.5ppm Experiment ’20/‘04 am- 11 659 000 ∙ 10-10 am- 11 659 000 ∙ 10-10 Achim Denig Radiative Return @ DAFNE MENU 2004

  6. ISR ds(e+ e- p + p- g) dMpp MC- Generator PHOKHARA = NLO J. Kühn, H. Czyż, G. Rodrigo Radiator-Function H(s) H(s) Radiative Return • Standard method for cross section measurement is the energy scan, i.e. the • systematic variation of the c.m.s.-energy of the accelerator • DAFNE is a f - factory and therefore designed for a fixed c.m.s.-energy: • s = mf = 1 019 MeV; a variation of the energy is not foreseen in near future Complementary approach: Take events with Initial State Radiation (ISR) “Radiative Return” to r(w)-resonance: e+ e- r(w) + g  p+ p- + g g r0 Cross section as a function of the 2-Pion invariant mass sp=Mpp2 sp Achim Denig Radiative Return @ DAFNE MENU 2004

  7. Background Luminosity Signal Acceptance Selections-Efficiency Analysis p+p-g • Final state e+e- p+ p- grelatively easy signature, however cross • section measurement on percent level is a challenging task (normali- • zation, efficiencies, background) • KLOE Detector designed for CP – violation, we are having a high • resolution tracking chamber ideal for the measurement of Mpp ! Analysis- Items: Achim Denig Radiative Return @ DAFNE MENU 2004

  8. Selection p+p-g Drift Chamber EM Calorimeter Pion tracks at large angles 50°< qp< 130° Photons at small angles qg< 15°andqg > 165° are shadowed by quadrupoles near the I.P. 500<  < 1300  NO PHOTON TAGGING  > 1650  < 150  • • High statistics for ISR events • Reduced background contamination • Low relative contribution of FSR Achim Denig Radiative Return @ DAFNE MENU 2004

  9. 2) Kinematic Separation f p+ p- p0 e+e- m+ m- g using „Trackmass“-variable Mpp – dependent MTRK-Cut 3) Residual Background Fit Trackmass-Spectra for signal and background withfree normalization parameters (shape from MC) Background p+p-g 1)Pion-Electron-Separation Rad. Bhabhas e+e- e+e- gare separated by means of a Likelihood- Method (Signature of EmC-Clusters and TOF of particle tracks) MTRK (MeV) p+p-p0 p+p-gg tail signal region mp m+m-g + e+e-g mm mr2 Achim Denig Radiative Return @ DAFNE MENU 2004

  10. Statistics:141pb-1 of 2001-Data 1.5 Million Events High Statistics! High Resolution! r-w Interference Analysis s(e+e- p+p-g) • Efficiencies: • - Trigger & Cosmic veto • Tracking, Vertex • p- e- separation • Reconstruction filter • Trackmass-cut • Unfolding resolution • Acceptance Errors: 0.9% • Background: • e+ e- e+ e-g • e+ e- m+ m- g • fp+ p- po 0.3% Luminosity: Bhabhas at large angles > 55°, seff = 430 nb, 0.3%exp 0.5%theo Achim Denig Radiative Return @ DAFNE MENU 2004

  11. Fp=1 s (ppg) mit Fp=1 sp (GeV2) Extraction s(e+e- p+p-) Radiator-Function (ISR): • ISR-Process calculated at NLO-level • Generator PHOKHARA(Kühn et.al) • Comparison withKKMC(Jadach et.al.) • Precision: 0.5% Radiative Corrections: i) Bare Cross Section divide by Vacuum Polarisation ii) FSR - Corrections Cross section spp must be incl. for FSR Vacuum Polarization Cross Section Radiative Return requires ISR photon  be inclusive for ISR-FSR-events e+ e- p+ p- gISR(gFSR) Achim Denig Radiative Return @ DAFNE MENU 2004

  12. Result published now • Considerable improvement • in near future Cross Section s(e+e- p+p-) Aim: Cross Section e+e- p+p- TOTAL ERROR 1.3% To be compared with 0.9% CMD-2 Error: exp.+syst.+stat. Achim Denig Radiative Return @ DAFNE MENU 2004

  13. Pion Formfactor 45 CMD-2 KLOE 45 40 35 30 25 20 • Comparison with CMD-2 in the Energy Range 0.37 <Mpp2<0.93 GeV2 15 10 1.3% Error (375.6  0.8stat  4.9syst+theo) 10-10 5 KLOE 0.9% Error 0 (378.6  2.7stat  2.3syst+theo) 10-10 CMD2 sp [GeV] 0.4 0.7 0.8 0.9 0.5 0.6 • KLOE data points are not in excellent but in a fair agreement • with CMD-2: KLOE higher at low sp and lower at large sp 2p Contribution to amhadr • Dispersions Integral for the 2-Pion-Channel in Energy Range 0.35 <Mpp2<0.95 GeV2 ampp = (388.7  0.8stat  3.5syst  3.5theo) 10-10 Achim Denig Radiative Return @ DAFNE MENU 2004

  14. Comparison with t Data Rel. difference of e+e--data with respect to t-data (avg.) At large values of sp (>mr) KLOE & CMD-2 deviate from t-Data> 10% unsufficient understanding of isospin breaking corrections in t-Data ?! Achim Denig Radiative Return @ DAFNE MENU 2004

  15. New Conclusions • Status of the anomalous magnetic moment of the muon today (August ’04): M. Davier, A. Höcker @ ICHEP04 • Including: • New KLOE data • New 4th order QED contribution • (Kinoshita) hep-ph/0402206 • New Light-by-light contribution • (Melnikov, Vainshtein) • hep-ph/0312226 • t – data excluded! Including KLOE • Theory (SM) - Experiment amexp - amtheo = ( 25.2 ± 9.2 ) ·10-10 2.7 “standard deviations” • KLOE has proven feasibility of the Radiative Return for high-precision hadronic cross section measurements: hep-ex/0407048, sent to Phys. Lett. B Achim Denig Radiative Return @ DAFNE MENU 2004

  16. Asymmetry [%] 20 • Data • MC 10 0 -10 K L O E P R E L I M I N A R Y -20 50 70 90 110 130 Polar Angle [°] Outlook: KLOE • Measure s(pp) in the region close to threshold, Mpp < 600 MeV, • responsible for 20% of ampp • This region excluded by angular selection in small angle photon approach • Complementary analysis at large photon angles • At large photon angles the amount of FSR is large! • test model of scalar QED (i.e. poinlike pions) •  MeasureCharge Asymmetry • and compare data with MC • Charge asymmetry is due to different • C-Parity of ISR- and FSR-amplitudes Achim Denig Radiative Return @ DAFNE MENU 2004

  17. dam (theor.)  3…4 · 10-10 dam (exp.) < 2…3 · 10-10 Actual Difference: 25 ± 9· 10-10 Future Outlook: Muon Anomaly Theory: • BaBar fills gap between DAFNE, VEPP-2M ( < 1.4 GeV ) and BES ( > 2 GeV) • and will measure all relevant exclusive channels (see e.g. hep-ex/0408078) • KLOE/CMD-2threshold region < 0.4 GeV2 • Future measurementsat BES, VEPP-2000, CLEO, BELLE, DAFNE-2? • “Real Theory“: Rad. corrections, Light-by-light-scattering, Isospin breaking ... Experiment: • New beam time for BNL-E821 (still limited by statistics)!? • Ambitious new project for 5th generation (g-2)m experiment at J-PARC Achim Denig Radiative Return @ DAFNE MENU 2004

  18. Work supported by: Emmy – Noether – Programm Achim Denig Radiative Return @ DAFNE MENU 2004

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